Microscope objective

ABSTRACT

A microscope objective comprising a small number of lenses by arranging a single lens made of glass of high refractive index and low dispersion as the first lens component, aberrations of said microscope objective being corrected quite favourably.

O United Sta [111 3,893,752

Tojyo 51 July 8, 1975 MICROSCOPE OBJECTIVE [56] References Cited [75]Inventor: Tsutomu Tojyo, Tokyo, Japan UNITED STA S PATENTS [73]Assignee: Olympus Optical Co. Ltd. Tokyo, 3,552,831 l/l97l Shoemaker350/176 Japan Primary Examiner-Paul A. Sacher Filed! y 1974 Attorney,Agent, or Firm-Cushman, Darby & 21 Appl. No.: 471,060 Cushma 0 F A r P iD ta [57] ABSTRACT [3 1 oregn pp canon ty a A microscope objectivecomprising a small number of May 18, 1973 Japan 48-56034 lenses yarranging a Single lens made of glass of g refractive index and lowdispersion as the first lens [52] US. Cl. 350/229; 350/176, 350/177Component, aberrations of Said microscope objective [51] Int. Cl G02b9/12; G02b 1/00 being Corrected quite favourably v [58] 1 Field ofSearch 350/229, 177, 176

1 Claim, 5 Drawing Figures MICROSCOPE OBJECTIVE BACKGROUND OF THEINVENTION 1. Field of the invention The present invention relates to amicroscope objective of the achromat class with the magnification about40x.

2. Description of the prior art Various microscope objectives of theachromat class with magnifications about 40x for which aberrations arefavourably corrected exist already. However, most of those conventionalmicroscope objectives comprise for example four lens components of sixlenses and, as the number of lenses is large, it was very difficult toreduce the cost of lens systems.

SUMMARY OF THE INVENTION It is, therefore, the primary object of thepresent invention to provide a microscope objective of the achromatclass with the magnification about 40x comprising a small number oflenses, i.e., three lens components of five lenses for which aberrationsare corrected quite favourably.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a sectional viewillustrating the lens arrangement'of the microscope objective accordingto the present invention; and

FIGS. 2A, 2B, 2C and 2D show graphs of aberration curves of thepreferred embodiment of the microscope objective according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to theaccompanying drawings, the concrete contents of the microscope objectiveaccording to the present invention are described below. The lens systemaccording to the present invention is arranged as shown in FIG. 1 andcomprises three lens components of five lenses in which the first lenscomponent is a positive meniscus lens with its concave surfacepositioned on the object side, the second lens component is a positivecemented doublet comprising a negative meniscus lens and a biconvexlens, and the third lens component is a positive cemented doubletcomprising a negative meniscus lens and a biconvex lens.

For conventional microscope objectives of this kind, a cemented lenscomponent is used as the first lens component. For the lens systemaccording to the present invention, however, a single lens is used asthe first lens component as mentioned in the above. By this arrangement,the number of lenses in the lens system as a whole is made smaller byone lens compared with that of conventional lens systems. When a singlelens is used as the first lens component as above, correction ofchromatic aberration may become considerably difficult. In the presentinvention, however, chromatic aberration is corrected favourably byusing glass of high refractive index and low dispersion or extraordinarydispersion, for which the refractive index is 1.75 or more and Abbesnumber is 55 or less, for the first lens component of the lens system.

Besides, when a single lens is used as the first lens component,aberrations other than chromatic aberration may also becomeunfavourable. For the lens system according to the present invention,however, those aberrations are also favourably corrected to the degreesame as or better than those of conventional microscope objectives ofthis kind by using the abovementioned new type of glass for the firstlens component and, at the same time, by adequately selecting glassmaterials for respective lenses of the second and third lens components,radii of curvatures of respective lenses, etc.

A preferred embodiment of the lens system according to the presentinvention is shown below.

Embodiment f= l, B=40X. NA 0.65, WD 0.168 r =-4.498

d 0.949 n, 1.7865 :1, 50.2 r 0.926

d =0.186 n 1.7847 u =25.7 r, 1.349

d =0.186 n.,= 1.8061 u,=40.8 r 1.318

where reference symbols r through r represent radii of curvatures ofrespective surfaces of lenses, reference symbols d, through d representthicknesses of respective lenses and spaces between lenses, referencesymbols n through n represent refractive indexes of respective lenses,reference symbols 11 through 11 represent Abbes numbers of respectivelenses.

For the above embodiment of the present invention, graphs of aberrationcurves are shown in FIGS. 2A, 2B, 2C and 2D. Out of these figures, FIG.2A shows spherical aberration, FIG. 2B shows OSC', FIG. 2C showsastigmatism and FIG. 2D shows distortion.

As it is evident from the above-mentioned embodiment and graphs of itsaberration curves, the microscope objective according to the presentinvention comprises a small number of lenses, i.e., three lenscomponents of five lenses, and its chromatic aberration and otheraberrations are corrected quite favourably. Besides, for the microscopeobjective according to the present invention, it is possible to make thework distance 10% to 15% longer compared with conventional microscopeobjectives of the achromat class with magnification about 40x.Therefore, the lens system according to the present invention is veryconvenient for practical use.

I claim:

1. A microscope objective comprising three lens components of fivelenses wherein the first lens component is positive meniscus lens withits concave surface positioned on the object side, the second lenscomponent is a positive cemented lens comprising a negative meniscuslens and a biconvex lens and the third lens component is also a positivecemented lens comprising a negative meniscus lens and a biconvex lens,said microscope objective having the following numerical values:

d 0.949 n, 1.7865 v, 50.2 r ().926

-Continued n, l.7847

sent Abbe's numbers of respective lenses.

1. A microscope objective comprising three lens components of fivelenses wherein the first lens component is positive meniscus lens withits concave surface positioned on the object side, the second lenscomponent is a positive cemented lens comprising a negative meniscuslens and a biconvex lens and the third lens component is also a positivecemented lens comprising a negative meniscus lens and a biconvex lens,said microscope objective having the following numerical values: